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This option has been initially in the mailserver.fullTextSearch scope. However, this option modifies the location of all index files of dovecot and not only those used by the full text search feature. It is then more relevant to have this option in the mailserver top level scope. Moreover, the default option has been changed to null in order to keep existing index files where they are: changing the index location means recreating all index files. The fts documentation however recommend to change this default location when enabling the fts feature.
69 lines
2.5 KiB
ReStructuredText
69 lines
2.5 KiB
ReStructuredText
Full text search
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==========================
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By default, when your IMAP client searches for an email containing some
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text in its *body*, dovecot will read all your email sequentially. This
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is very slow and IO intensive. To speed body searches up, it is possible to
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*index* emails with a plugin to dovecot, ``fts_xapian``.
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Enabling full text search
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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To enable indexing for full text search here is an example configuration.
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.. code:: nix
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{
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mailserver = {
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# ...
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fullTextSearch = {
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enable = true;
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# index new email as they arrive
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autoIndex = true;
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# this only applies to plain text attachments, binary attachments are never indexed
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indexAttachments = true;
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enforced = "body";
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};
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};
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}
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The ``enforced`` parameter tells dovecot to fail any body search query that cannot
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use an index. This prevents dovecot to fall back to the IO-intensive brute
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force search.
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If you set ``autoIndex`` to ``false``, indices will be created when the IMAP client
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issues a search query, so latency will be high.
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Resource requirements
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~~~~~~~~~~~~~~~~~~~~~~~~
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Indices created by the full text search feature can take more disk
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space than the emails themselves. By default, they are kept in the
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emails location. When enabling the full text search feature, it is
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recommended to move indices in a different location, such as
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(``/var/lib/docecot/indices/%d/%n``) by using the option
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``mailserver.indexDir``.
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.. warning::
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When the value of the ``indexDir`` option is changed, all dovecot
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indices needs to be recreated: clients would need to resynchronize.
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Indexation itself is rather resouces intensive, in CPU, and for emails with
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large headers, in memory as well. Initial indexation of existing emails can take
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hours. If the indexer worker is killed or segfaults during indexation, it can
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be that it tried to allocate more memory than allowed. You can increase the memory
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limit by eg ``mailserver.fullTextSearch.memoryLimit = 2000`` (in MiB).
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Mitigating resources requirements
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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You can:
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* disable indexation of attachements ``mailserver.fullTextSearch.indexAttachments = false``
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* reduce the size of ngrams to be indexed ``mailserver.fullTextSearch.minSize`` and ``maxSize``
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* disable automatic indexation for some folders with
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``mailserver.fullTextSearch.autoIndexExclude``. Folders can be specified by
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name (``"Trash"``), by special use (``"\\Junk"``) or with a wildcard.
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